Image Diffraction in Camera Lens

Image Diffraction in Camera Lens

When the light forming an image passes
through a lens aperture, the wave front is distorted in much the same
way as an ocean wave is distorted as it passes through an opening in a
breakwater. The result is reduced image resolution or picture
sharpness. The smaller the aperture or the higher the f-number will
result even more distortion. This distortion effect is called image
diffraction.

Diffraction, being produced by the
presence of the lens aperture (usually an iris diaphragm) rather than
by refractive qualities of the lens, is not itself a lens aberration.
However, since all camera lenses have an aperture, and since
diffraction impairs image quality, photographers must take it into
account.

Closing the lens aperture to reduce the
effects of residual lens aberrations introduces image diffraction.
Diffraction itself can only be reduced by widening the aperture (that
is, using a lower f-number).

Therefore, camera lenses have an optimum
aperture: a point beyond which further closing down will introduce
diffraction more than it will correct aberrations. This optimum
aperture differs from lens to lens, but usually occurs between f/4 and
f/8.

Fortunately, because its onset is
relatively gradual, diffraction is not a serious problem in most
photography. It is more of a problem in technical photography, where
the optimum lens aperture must be determined for very critical
sharpness. The most drastic effects occur at very small apertures; a
sharp drop in lens performance occurs after about f/90 to f/128. Since
few, if any, lenses are calibrated to such small apertures, the worst
effects are limited to high-magnification photograph and close-up
photography.

BasicCameraPhotography.com is a participant in the Amazon Serivce LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com